In recent years, from the viewpoint of environmental protection, emission reduction of exhaust gas from an internal combustion engine (hereinafter referred to as “engine” in some cases) mounted on a vehicle and improvement in fuel consumption rate (fuel consumption) are desired. As a vehicle that satisfies these requirements, a hybrid vehicle on which a hybrid system is mounted has been put into practical use. The hybrid vehicle includes an engine such as a gasoline engine and a diesel engine and a running motor (for example, constituted by a motor-generator or a motor). The running motor is driven by electric power generated due to the output of the engine or by electric power stored in a running battery. The hybrid vehicle runs using one or both of the engine and the running motor as a running drive-force source.
In recent years, a hybrid vehicle (what is called a plug-in hybrid vehicle) that can charge the running battery for supplying electric power to the running motor by electric power from a power supply (outside power supply) outside of the vehicle, for example, a household power supply is being developed.
This plug-in hybrid vehicle is designed on the assumption of running preferentially using the electric power from the running battery, in order to significantly improve the fuel consumption rate. For example, as disclosed in Patent Literature 1 and Patent Literature 2 below, the running mode of the plug-in hybrid vehicle is set to a mode (generally referred to as “charge depleting (CD) mode” or “electric vehicle (EV) mode”) that preferentially performs running using the power of the running motor alone until the electricity storage amount in the running battery is reduced up to a predetermined value. The running mode transitions to a mode (generally referred to as “charge sustain (CS) mode” or “hybrid vehicle (HV) mode”) that preferentially performs running using both powers of the engine and the running motor when the electricity storage amount in the running battery becomes less than the predetermined value.
In this plug-in hybrid vehicle, for running with the power of the running motor alone in the CD mode, the possible running distance with the current electricity storage amount (remaining electricity storage amount) in the running battery is calculated and this information is displayed on a meter panel (instrument panel). More specifically, the electric mileage is calculated from the running condition in the past (relationship between the amount of electric power consumption and the running distance) (electric-mileage learning is performed). This electric mileage is a running distance per unit electric energy. Subsequently, this electric mileage is multiplied by the electricity storage amount (the electric energy that can be used until the electricity storage amount reaches the predetermined value at which the mode transitions to the CS mode) in the running battery, so as to calculate the possible running distance.
The following Patent Literature 3 discloses that, in the case where EV running (running using the power of the running motor alone) is performed, the electric energy required for this EV running and the usable electric energy are compared with each other to calculate a possible EV running distance so as to determine to continue the EV running or cause the transition to HV running (running using both powers of the engine and the running motor).